syn-Propanediaw S-oxide (C3H6OS), a member of a cwass of organosuwfur compounds known as diocarbonywS-oxides (formerwy "suwfines"),[2] is a wiqwid dat acts as a wachrymatory agent (triggers tearing and stinging on contact wif de eyes). The chemicaw is reweased from onions, Awwium cepa, as dey are swiced. The rewease is due to de breaking open of de onion cewws and deir reweasing enzymes cawwed awwiinases, which den break down amino acidsuwfoxides, generating suwfenic acids. A specific suwfenic acid, 1-propenesuwfenic acid, formed when onions are cut, is rapidwy rearranged by a second enzyme, cawwed de wachrymatory factor syndase or LFS, giving syn-propanediaw S-oxide.[3] The gas diffuses drough de air and, on contact wif de eye, it stimuwates sensory neurons creating a stinging, painfuw sensation, uh-hah-hah-hah. Tears are reweased from de tear gwands to diwute and fwush out de irritant.[4] Recentwy, a structurawwy rewated wachrymatory compound, syn-butanediaw S-oxide, C4H8OS, has been found in anoder genus Awwium pwant, Awwium sicuwum.[5]